1. Field of the Invention
This invention relates to co-boresighted dual-mode SAL/IR seekers for projectiles, missiles, and other ordnance that engage targets by detecting and following semi-active laser (SAL) energy scattered from the targets and detecting passive infrared (IR) emissions from the targets.
2. Description of the Related Art
Laser guided ordnance is commonly used to engage point targets with a high probability of success and minimal collateral damage. Such ordnance includes guided artillery projectiles, guided missiles, and guided bombs, all of which will be referred to herein as “projectiles”.
A laser guided projectile typically includes a semi-active laser (SAL) seeker to detect laser radiation scattered from the intended target and to provide signals indicative of the target bearing such that the projectile can be guided to the target. The SAL may include a non-imaging optical system to capture and focus the scattered laser radiation and a position-sensitive detector e.g. a quad-detector. The optical system may convert the target bearing to an irradiance distribution or “spot” positioned on the detector. As the target bearing changes the position or spatial displacement of the spot changes. The detector produces at least one guidance signal in response to the position of the spot as a measure of target bearing.
U.S. Pat. No. 6,924,772 entitled “Tri-mode co-boresighted seeker” describes a tri-mode co-boresighted seeker including a primary collecting mirror assembly having a parabolic surface and a forwardly located dielectric secondary mirror assembly including a dielectric mirror coating which reflects infrared (IR) energy to an IR detector assembly located on a central longitudinal axis on one side of the secondary mirror while providing substantially unobstructed propagation of millimeter wave RF energy and laser energy in a joint or common signal path there through to means located on the other side of the secondary mirror for extracting and diverting laser energy away from the common RF-optical signal path to a laser sensor assembly while causing little or no disturbance to the RF signal as it propagates to a co-located bifurcated waveguide assembly which couples the RF energy to an RF sensor means located behind the primary mirror.